Patient controlled analgesia device

ABSTRACT

A mechanical patient-controlled analgesia device for injecting medicine into a patient&#39;s IV, includes an IV reservoir and a syringe communicated to the IV reservoir and having a syringe plunger. A mechanical biasing element is provided for exerting bias on the syringe plunger in a first syringe-filling direction to draw medicine from the IV reservoir into the syringe. An injection plunger is operable by the patient to move the syringe plunger in a second injection direction against the bias to inject the medicine in the syringe into a patient&#39;s IV. The injection plunger is movable independently of the syringe plunger and is engaged with but unconnected to the syringe plunger when the patient moves the injection plunger to inject the medicine. The patient can inject only a calibrated amount of medicine drawn into the syringe as determined by calibration of the biasing element and a metering element for a given viscosity of the medication.

RELATED APPLICATION

This application is a division of copending U.S. application Ser. No.13/815,405 filed Feb. 28, 2013, which claims benefits and priority ofU.S. provisional application Ser. No. 61/607,832 filed Mar. 7, 2012, theentire disclosures of both of which are incorporated herein byreference.

FIELD OF THE INVENTION

This invention relates generally to a patient controlled analgesia (PCA)device and, more specifically, to a mechanical, low cost, and disposablePCA that allows a patient to titrate their own pain medication.

BACKGROUND OF THE INVENTION

Pain is common in emergency medicine. The most effective drugs forsevere pain are narcotic analgesics. Narcotics must be givenintravenously in order to have rapid effect. Narcotics haveidiosyncratic effects and their effects vary widely between patients.Therefore, it is difficult to predict what dose is appropriate for aspecific patient.

Narcotics are most commonly used to ease pain and are (and mostappropriately) titrated to effect. This means that small doses are givenfrequently until the patient has an adequate response. Since pain reliefand most side effects are subjective, this means that doses arecontinued until the patient stops requesting more and says they have hadenough. In practice, this procedure is difficult and time consuming; asa result, most patients do not receive optimal doses, because if thedoses are made small enough and the intervals between them long enoughto be safe, titration can easily take a half hour. Because of lengthytitration periods, either a nurse or other provider stays at the bedsideduring the entire period or the titration is slowed (meaning longerwithout pain relief) or larger doses/shorter time periods are used(which decreases safety). Using morphine as an example, 2 mg (a safedose) every 3 minutes (just long enough to get from arm to brain) to 20mg (a reasonable loading dose) takes 30 minutes.

There is also considerable evidence that when medical staff give painmedications only when patients ask, the patients rarely get enough; acondition known as oligo-analgesia. Worse, this often results inintermittent overdosing. Patients commonly alternate between pain andover sedation when these “prn” orders are used.

The solution to this problem is Patient Controlled Analgesia machines,or PCAs. Current PCAs are electro mechanical devices that patients useto inject their own pain medications when they want them. PCAs reduceboth oligo-analgesia and sedation, and patients use less narcoticsoverall and recover faster.

PCAs are the standard of care on post-operative units, but are rarelyused in emergency departments or similar areas. This is because PCAs arequite complicated. PCAs must be individually programmed for eachpatient. Programming must include dose and interval between doses plus a“lock-out” period. For example: the protocol might be “morphinesulphate, 2 mg every 5 minutes but no more than 10 mg per hour or 20 mgevery 4 hours”. This is necessary and useful during a prolongedpost-operative stay, particularly since patients are loaded withmedication in the post anesthesia recovery area prior to moving to theward. In addition, PCAs require the medication to be used in a specificcontainer; in this case morphine might be available only in a 30 mg prefilled vial specific for the kind of PCA machine used. For obviousreasons, PCAs require redundancy and fail safe mechanisms. As a result,PCA's are expensive, fragile, and time consuming to set up.

What is needed is a PCA that is specific to the needs of the emergencypatient. Since emergency patients start with no pain medication, andbecause they rarely stay for more than a few hours, what is reallyneeded is a device that they can use to titrate their own loading dose.For emergency patients, maintenance doses are not the issue that theyare for admitted patients. The device needs to be quick and easy to setup and use so patients do not need to wait in pain for programming totake place.

SUMMARY OF THE INVENTION

To this end, the present invention provides a patient-controlledanalgesia (PCA) device, especially for use with emergency patients,although the invention is not limited to emergency patient use. In anillustrative embodiment of the present invention, PCA device comprisesan IV (intravenous) medication reservoir, a syringe communicated to thereservoir and having a syringe plunger, a biasing element, such as forexample a compression spring, for exerting bias on the syringe plungerin a first, syringe-filling direction to draw medication from the IVreservoir into the syringe, and an injection plunger operable by thepatient to move the syringe plunger in a second injection directionagainst the bias to inject the medication in the syringe into apatient's IV. The injection plunger is movable independently of thesyringe plunger and is engaged with but unconnected to the syringeplunger when the patient moves the injection plunger to inject themedication. As a result, the patient can use the injection plunger toinject the calibrated amount of medication in the syringe into thepatient's IV but cannot use the injection plunger to draw medicationfrom the IV reservoir into the syringe.

In a particular embodiment of the present invention, the syringe iscommunicated to the IV medication reservoir by a metering element andhas a syringe plunger which travels under bias of the biasing element inthe first, syringe-filling direction to draw medicine from the IVmedication reservoir into the syringe wherein the metering element andthe biasing spring are calibrated to permit a only calibrated amount ofmedication to be drawn for a given time into the syringe from the IVmedication reservoir. The patient can inject only this calibrated amountof medication into the patient's IV since the calibrated amount isdetermined by the biasing element and metering element for a givenviscosity of the medication.

The present invention also envisions a PCA method of injecting medicineinto a patient's IV comprising the steps of drawing medicine from an IVmedication reservoir into a syringe using a biasing element that exertsbias on a plunger of the syringe in a first, syringe-filling directionto draw medication into the syringe and then injecting the medicine inthe syringe into the patient's IV by the patient's operating theinjection plunger that engages but is unconnected to the syringe plungerto move the syringe against the bias in a second injection direction.

The PCA device and method pursuant to the present invention areadvantageous especially for use by the emergency patient. The PCA deviceand method provides quick and easy set-up and use. Since emergencypatients start with no pain medication, and because they rarely stay formore than a few hours, the patient can use the PCA device to titratetheir own loading dose so the patient does not need to wait in pain forprogramming to take place.

These and other advantages will become more apparent from the followingdetailed description taken with the following drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an illustrative embodiment of a mechanical PCA, accordingto an illustrative embodiment of the present invention.

FIG. 2 is an enlarged schematic view of the IV medication reservoirmetering element and one-way valves when fluid/medication is being drawnfrom the reservoir into the syringe (valve from reservoir is open andvalve to patient is closed).

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 and 2 schematically depict an illustrative embodiment of themechanical PCA offered for purposes of illustration and not limitationas comprising a medication reservoir 8, such as, for example, aconventional IV medication bag 10, and a conventional syringe 12communicated to the IV bag 10. The IV bag 10 is disposed in thecontainer 13 and shown supported on the container bottom for purposes ofillustration and not limitation. The syringe 12 is disposed in thecontainer 13 and is fixedly supported by brackets B or other support incontainer 13. The container 13 includes an opening 13 a that allowsambient air to flow into and out of container 13 and a closeable door(not shown).

The IV reservoir 10 is filled via injection port 10 a with medication oris preloaded with medication. The container door can be latched shutafter a preloaded bag is in position or after medicine is added to theIV bag in the container. The IV reservoir 10 also includes or isconnected to a metering element 14 that participates in flow ratecontrol of the medication in the IV reservoir into the syringe asexplained below. For purposes of illustration and not limitation, the IVreservoir 10 can be a commercially available IV bag. The meteringelement 14 can comprise, but is not limited to, a capillary tube, ametering needle valve, or a combination thereof.

The syringe 12 includes a syringe plunger 16 which is biased by a springbiasing element 18 in an upward (first) syringe-filling direction todraw fluid medicine from the IV reservoir 10 into the syringe when thesyringe plunger 16 is moved upwardly. The metering element 14 and thebiasing element 18 are calibrated to permit a calibrated amount ofmedication to be drawn for a given time (e.g. 5 ml in two minutes) intothe syringe from the IV medication reservoir. For purposes ofillustration and not limitation, the syringe 12 with plunger 16 can be acommercially available syringe.

For purposes of illustration, the biasing element 18 is shown comprisinga compression coil spring 20, which resides around the shaft of thesyringe plunger 16 and between an outer spring retainer end 16 a of thesyringe plunger 16 and a fixed spring support member 22, which isaffixed to the container 13. However, the biasing element 18 cancomprise an elastic or resilient plastic or rubber sleeve, or otherbiasing element that can exert an upward bias on the syringe plunger 16in FIG. 1.

Referring to FIG. 1, a patient-operated injection plunger 24 is showndisposed above the syringe plunger 16 and operable by the patient tomove the syringe plunger 16 in a downward injection (second) directionagainst the bias of the biasing element 18 to inject the medication inthe syringe into a patient's IV. The injection plunger 24 is movableupwardly and downwardly independently of the syringe plunger 16 and isengaged with but unconnected to the syringe plunger 16 when the patientmoves the injection plunger to inject the medicine. To this end, theinjection plunger 24 includes an outer patient-operable end 24 adisposed outside the container 13 and an inner lower end 24 b inside thecontainer 13 that engages but is unconnected to outer upper end 16 a ofthe syringe plunger 16. The inner lower end 24 b of the injectionplunger 24 rests on, but is unconnected to, the outer upper springretainer end 16 a of the syringe plunger 16 so as to follow its movementup and down in response to bias of the biasing element 18 (spring 20),except when the patient pushes the injection plunger 24 downwardly orpulls it upwardly. The inner lower end 24 b of the injection plungerduring its upward movement eventually abuts a stop 17 that is fixedlydisposed on the container.

The IV medication reservoir 10 is connected or communicated to syringe12 via a one way valve 30 that allows the biasing element 18 to drawmedicine from the reservoir 10, but closes under pressure so that fluidmedication does not flow from syringe 12 to back to the IV reservoir 10and a second one way valve 32 that allows the syringe plunger 16 to pushmedication from the syringe 12 into patient's IV but prevents flow of IVfluid/medication from the patient's IV back into the syringe. FIG. 2illustrates schematically the one way flapper valves 30 and 32 andmetering element 14. The one-way valves 30, 32 can include, but are notlimited to, ball check valves, conical check valves, or flapper valves.

In practice of a method embodiment of the present invention, the IVmedication reservoir 10 is filled via injection port 10 a withmedication and injection fluid as needed (collectively designated M inFIG. 1) and connected to syringe 12 via metering element 14 and one wayvalves 30 and 32. The door of box or container 13 is closed and locked.The biasing element 18 (e.g. compression spring 20) and metering element14 (e.g. capillary tube) are calibrated to allow a specific amount ofmedicine to flow into the syringe per unit time (e.g., 5 ml in twominutes), corresponding to a maximum amount of medication ordered perunit time. Different mechanical PCAs can be designed to give differentvolumes of fluid with each injection, and the biasing element 18 (e.g.spring 20) and metering element 14 are calibrated for each one.

Thus, the mechanical properties of the illustrated PCA device (e.g.spring, capillary tube radius for a given fluid viscosity) limit thedose per time interval. The difference between the height of the springbiasing element 20 when fully compressed and the height of the springbiasing element 20 when fully extended as determined by the fixed stop17 determines the maximum amount of medication drawn into the syringe12, and hence the maximum dose injected at one time. A differentspring/metering element (restrictor) combination can be selected andused in order to adjust the particular volume of fluid/medication foreach injection. The biasing element 18 (e.g. spring 20) and meteringelement (restrictor) 14 are calibrated for each combination.

The syringe 12 cannot fill more rapidly than the biasing element 18(spring 20) and restricting needle or capillary tube allow for a givenfluid viscosity of the medication. Even doubling the spring force alonehas relatively little effect on filling time. The injection plunger 24touches, but does not connect to, the syringe plunger 16, so drawing theinjection plunger back (upwardly in FIG. 1) does not fill the syringe.Since the viscosity of water soluble medications approximate that ofwater a single biasing element and metering element (restrictor)combination can be used for multiple medications.

Once the syringe is filled, the patient simply pushes the injectionplunger 24 downwardly to inject the calibrated amount of medication intothe patient's IV. Since the injection plunger 24 is not connected to thesyringe plunger 16, the injection plunger cannot be used to pullmedication into the syringe 12. Thus, the patient's pressing on theinjection plunger cannot cause more than the specified amount ofmedication to be injected per unit time.

The PCA device described above may be fabricated of conventional medicalparts (syringe, restricting needle, connecting tubing, valves and IVmedication bag), but using components specifically designed for the PCAdevice could make it simpler and easier to set up. The PCA device thuscan be very low cost and hence disposable. The above-describedembodiments of the PCA device do not comprise any electrical orelectro-mechanical parts, although such parts may be incorporated intothe PCA device. For example, the biasing element 18 may be replaced byan electrical or electromechanical (solenoid) biasing device.

The PCA device has potential uses in pre-hospital (ambulance) care,acute/urgent care clinics, emergency departments and other sites whereloading doses of medications are given to treat acute pain and prior topainful procedures.

It is noted that, as used in this specification and the appended claims,the singular forms “a,” “an,” and “the,” include plural referents unlessexpressly and unequivocally limited to one referent. Thus, for example,reference to “a PCA” includes two or more different PCAs. As usedherein, the term “include” and its grammatical variants are intended tobe non-limiting, such that recitation of items in a list is not to theexclusion of other like items that can be substituted or other itemsthat can be added to the listed items.

Upon studying the disclosure, it will be apparent to those skilled inthe art that various modifications and variations can be made in thedevices and methods of various embodiments of the invention. Otherembodiments will be apparent to those skilled in the art fromconsideration of the specification and practice of the embodimentsdisclosed herein. It is intended that the specification and examples beconsidered as examples only. The various embodiments are not necessarilymutually exclusive, as some embodiments can be combined with one or moreother embodiments to form new embodiments.

I claim:
 1. A method of injecting medication into a patient's IV underpatient control, comprising providing a syringe having a syringe plungerwith an injection plunger that engages but is unconnected to the syringeplunger in a common syringe housing so as to be movable independently ofthe syringe plunger by the patient pulling in a first syringe-fillingdirection thereby separating the injection plunger from the syringeplunger in the syringe housing so that the patient cannot fill thesyringe with medication, using a biasing element that exerts a bias onthe syringe plunger in the first syringe-filling direction to drawmedication into the syringe, and then injecting the medication in thesyringe into the patient's IV by the patient's moving the injectionplunger in a second injection direction in engagement with the syringeplunger in the syringe housing to move the syringe plunger against thebias of the biasing element.
 2. The method of claim 1 wherein thepatient pushes the injection plunger in the second injection directionin engagement with the syringe plunger to move the syringe plungeragainst the bias of the biasing element.
 3. The method of claim 2wherein the patient's pulling of the injection plunger in the firstsyringe-filling direction cannot draw medicine into the syringe as aresult of the injection plunger being separated from the syringe plungerwhen the injection plunger is moved in the first syringe-fillingdirection.